The invention generally relates to structures and methods for increasing articulation in a vehicle, and more particularly, to hinged shackles for connecting leaf spring suspension assemblies to the frame of an off road vehicle.
Vehicles designed, built and marketed for off road use are increasingly being driven in more severe off road applications, while also being driven on paved highways and streets. One type of more severe off road driving is xe2x80x9crock crawling,xe2x80x9d which is commonly referred to as slowly driving a four wheel drive vehicle over through or between natural or even man made obstacles of a wide variety of shapes, angles, heights, widths, depths, compositions, etc. Such natural obstacles may include rocks, gulleys, ravines, stream beds, inclines or drops, among other things. Rock crawling refers not only to traversing the typically uneven rock surfaces, but also a variety of natural and man made surface material, including gravel, sand, dirt, concrete or metal barriers, and vegetation including exposed roots and tree stumps.
Rock crawling, and other types of off road use, can place severe demands on the suspension system to the vehicle. To maximize traction and control, it is generally advantageous to maintain each tire in full contact with the surface being driven, or at least as many tires and as much of each tire as possible. Similarly, it is also generally advantageous to keep the weight of the vehicle evenly distributed over each of the tires, or at least as much as possible. Because each axle of most non-military off road vehicles extend to at least one wheel on each side, driving on an uneven surface often means one wheel is significantly lower than the other, resulting in one or more tires losing maximum contact, or even being lifted off the surface. This is an even greater issue when the front and rear axles are at different levels or even at different angles. The relative ability of a vehicle to keep the tires on the ground during such maneuvering is commonly referred to as the articulation of the vehicle.
Off road vehicles commonly employ either a leaf spring or a coil spring suspension system to suspend the vehicle over the axles. Generally, in a leaf spring suspension system, a series of elongated bands of metal, or leaves, of varying lengths are stacked and banded together. One end of the assembly is bolted or otherwise fixed to the bottom of the vehicle, typically towards the center of the vehicle and away from the axle to be suspended. In a stock configuration, the leaves are commonly positioned under the axle, with a shallow U-shaped arc extending towards the outside of the vehicle. The end of the leaves near the outside of the vehicle typically terminates with a spring eye that allows a connection to a movable bar or shackle or other device that in turn is connected to the vehicle. One such leaf spring assembly is installed near each wheel. When at rest or under compression, the conventional leaf spring assembly typically presses the shackle up against the vehicle frame.
During compression of the leaf spring, this type of suspension allows the leaf spring to flatten and move toward the direction of the shackle. When the leaf spring is required to droop, or stretch as far as possible, it is restricted by the flex of the leaf spring itself. For this type of primarily vertical suspension, the bolted inner end of the leaf spring and the plates that make up the shackle limit the amount the leaf spring assembly can move.
The conventional leaf spring assembly is limited in articulation, e.g., when one side of the axle compresses and the other side does not compress as much, does not compress at all, or is required to droop. The axle is no longer level and the vehicle tilts. Because the leaf spring at the inner end is bolted and at the outer end has only limited vertical and forward movement, but no lateral movement, the leaves themselves must twist or flex to try to accommodate the changing lateral angle between the axle and the vehicle. Reliance on the leaf spring twisting not only limits articulation, but also can cause metal fatigue in the leaf spring assembly and result in premature failure.
To increase articulation, several modifications to leaf spring assemblies have been attempted, generally by allowing the leaf spring to more readily drop away from the frame. For example, in one configuration, the inner end of the leaf spring remains bolted to the vehicle frame and the spring eye remains connected to a shackle. However, the arm of the shackle is lengthened, which provides more droop. Although this configuration provides enhanced vertical suspension, it still relies on the leaf springs to twist to provide articulation. Also, lengthening the arm of the shackle generally reduces the lateral stability of the vehicle, particularly at higher speeds.
In another design, known as a folded hinged shackle, the shackle has a first arm with one end connected to the vehicle and the other end pivotally connected to a second arm, that in turn is connected to the spring eye of the leaf spring. When at rest or under compression, the folded hinged shackle is pressed up against the vehicle and the leaf springs primarily provide for compression. When the leaf spring is required to droop, however, the folded hinged shackle opens, providing increased droop. Again, articulation is limited by the amount of twisting of the leaf springs.
Another attempt to increase articulation is commonly referred to as a xe2x80x9cbuggy springxe2x80x9d suspension. Again, the end of the leaf spring towards the center of the vehicle is bolted to the vehicle frame. The outer shackle is replaced essentially with a second, shorter leaf spring assembly. The end of the shorter leaf spring assembly towards the center of the vehicle is bolted to the vehicle between the spring eye of the main leaf spring and the axle. The end of the shorter leaf spring assembly near the outside of the vehicle is connected to the spring eye of the main leaf spring by a conventional shackle design. This buggy spring assembly provides another level of vertical suspension and may provide more droop. It also increases articulation, as both the main and the shorter leaf springs will twist somewhat. However, articulation is still limited by the amount of twisting of the leaf springs. As with lengthening the shackle arm, replacing the shackle with a second leaf spring assembly generally reduces the lateral stability of the vehicle, particularly at higher speeds.
A more complicated assembly to try to increase articulation, known as a xe2x80x9cfour linkxe2x80x9d suspension, is commonly installed to greatly increase droop of the rear axle. This assembly again has the inner end of the leaf spring bolted to the vehicle, but is inverted, i.e., the leaf spring forms a concave shape opening downward. The outer end of the leaf spring extends only just past the axle and is not fixed to another component. Rather, it merely rests on top of the axle. To protect the vehicle from the slapping of the leaf springs, a small bumper is commonly inserted on the vehicle frame between the two ends of the leaf spring. The relative vertical drop is controlled by a four arm link system, with two arms for each side of the axle. One arm is pivotally connected to the outer end of the vehicle and extends to rest under the axle. A shorter arm is pivotally connected toward the inside of the longer arm and extends to suspend above the axle. The inverted leaf springs provide compression and the arms can be set to provide little or no pressure, resulting in very large amounts of droop if both sides of the axle are required to droop. This four link assembly is commonly used in faster off road races with big, fast jumps requiring large droop of both rear wheels. The rear axle essentially is momentarily free hanging, supporting little or no weight of the vehicle. In part because one end of the leaf spring is unattached, articulation is increased, although it is still limited by the amount of twist of the leaf springs. Again, the four link system reduces the lateral stability of the vehicle, particularly at the higher speeds on the road.
A more simple approach to increase articulation is to simply move the leaf springs of a conventional leaf spring assembly from under the axle to over the axle. This is commonly referred to as a xe2x80x9cspring overxe2x80x9d suspension or a xe2x80x9clift,xe2x80x9d as it literally lifts the body of the vehicle several inches relative to the axle. Because the leaf springs are above the axle, they are able to flatten more during compression and may twist more to increase articulation. However, the amount of articulation is still limited by the amount of twist of the leaf springs. Also, the increased ability of the leaf spring to twist and the raised center of gravity reduces the lateral stability of the vehicle.
Another more complicated approach, known as a xe2x80x9cxc2xe ellipticalxe2x80x9d suspension, uses the spring over suspension, leaving the leaf springs unattached to the axle. Instead, a long arm is pivotally connected at the outer end of the vehicle and extends to rest under the axle. A shorter arm connected to the longer arm extends to suspend above the axle. As with the four link system, the leaf springs provide compression and the arms can be adjusted to provide little or no pressure, resulting in very large amounts of droop if both sides of the axle are required to droop. Articulation is increased, but still is limited by the twist or flex of the leaf springs.
Many other attempts have been made to increase the articulation of off road vehicles, particularly leaf spring assemblies of four wheel drive vehicles and all terrain vehicles. Nonetheless, a need exists for a new or modified leaf spring assembly and method to increase articulation, while decreasing the lateral twisting forces of the leaf springs. A further need exists to provide such an assembly and method that is sufficiently stable to allow the vehicle to be driven both off road and on road.
The present invention is directed to a structure and method for increasing articulation of a vehicle. In one embodiment of the invention, a shackle comprises a first section having a proximal end and a distal end for connection to a vehicle, a second section having a proximal end connected to the proximal end of the first section and a distal end, a third section having a proximal end rotatably connected to the distal end of the second section and a distal end for connection to a suspension assembly of the vehicle.
A further embodiment of the invention is directed to a shackle for suspension assemblies in vehicles comprising a first section having a first leg, a second leg and a piece connecting he first and second legs. The first and second legs each comprise a distal end for connection to the frame of a vehicle and a proximal end that is rotatably connected to the proximal end of a second section. The second section further comprises a cylindrical distal end that is rotatably connected to the cylindrical proximal end of a third section. The third section also comprises a distal end for connection to the suspension assembly of the vehicle.
Yet another embodiment of the invention comprises a method for articulating a vehicle comprising rotating at least part of the suspension in a direction substantially parallel to the axle of the vehicle.